The invention relates to a factory scale apparatus for carrying out a hydrogenation reaction.
Hydrogenation reactions are frequently carried out in the presence of a pyrophoric catalyst such as Raney nickel. This presents a serious difficulty because flammable liquids such as methanol or ethanol are often used as hydrogenation solvents. The removal of the catalyst from the reaction mixture after the hydrogenation reaction is complete, presents serious difficulties. Generally the reaction mixture is passed through a filter, the catalyst is filtered out and removed in a closed circuit.
Handling of the resultant catalyst presents difficulties and the commonly used multiplate filters, which necessitate generation of hazardous dry material, require extensive safety precautions, and extended operation times to facilitate safe removal of the catalyst.
U.S. Pat. No. 4,021,354 describes a pressure filter comprising an outer casing having a filter basket supported therein. The filter basket comprises a tubular imperforate metallic shell with a sintered stainless steel filter disc welded to the lower end of the shell. Such a pressure filter is not suitable for use with fine metallic catalyst as the sintered disc readily clogs during operation. Removal of catalyst from the pores requires reverse flow of water and frequent use of acid to dissolve trapped material.
DE-A-3136905 describes a pressure filter including a sieve basket of the same type as that described in U.S. Pat. No. 4,021,354 and similar disadvantages apply.
There is therefore a need for an improved cost effective filter apparatus for removing a pyrophoric catalyst which will overcome these problems.
According to the invention there is provided a filter apparatus for recovery of spent hydrogenation catalyst-rich material, the apparatus comprising:
(a) a pressure filter container;
(b) the container having a filter plate mounted therein on which pyrophoric catalyst-rich material is filtered;
(c) the container having a catalyst inlet for pyrophoric catalyst-rich material to be filtered and an inlet for delivery of solvent or water to wash the spent catalyst on the filter plate; and
(d) a filter bag of solvent/water permeable material mounted in the container and supported on the filter plate for collection of filtered spent pyrophoric catalyst material in a water-wet form.
In a preferred embodiment the filter bag is of flexible material allowing easy fitting and removal from the filter. The bag can be folded into a compact size for disposal when required. Ideally the bag is of multifilament woven material. This ensures a large multilayer filter surface area which is not prone to blockage.
In a particularly preferred embodiment of the invention the bag is of acid resistant polypropylene multifilament weave. Thus if blockages occur the filter can be reversed and flushed with high pressure water and if necessary soaked in dilute HCl acid. Alternatively, the bags may be replaced at a predetermined frequency.
In one embodiment the filter bag is releasably mounted to the container. Preferably the filter apparatus includes releasable mounting means for tightening and demounting the filter bag from the container. The bag may be fitted with sewn lifting straps and removed by hoist into drums for off-site recovery of catalyst.
The filter container is preferably mounted on a transportable chassis. Preferably the chassis is a wheeled chassis.
The apparatus may be used in a batch process for carrying out a hydrogenation reaction comprising the steps of:
(a) mixing a pyrophoric catalyst with reactants and solvents to form a reaction mixture in a reaction vessel;
(b) adding hydrogen to the reaction vessel;
(c) after hydrogenation, removing the desired hydrogenation product from the reaction vessel;
(d) delivering the pyrophoric catalyst-rich material from the reaction vessel to a pressure filter;
(e) adding water to the pyrophoric catalyst-rich material in the filter; and
(f) removing the spent pyrophoric material from the pressure filter in a water wet form.
In a preferred embodiment of the invention the pressure filter is a single plate pressure filter, the catalyst being held in the filter in a water wet form.
In one embodiment the catalyst is Raney nickel.
Preferably the contents of the reaction vessel are decanted after hydrogenation, the desired hydrogenation product being substantially removed while allowing the catalyst-rich material to settle at the bottom of the vessel.
Preferably the reaction vessel is an agitated vessel, the agitator being stopped to allow the catalyst to settle at the bottom of the vessel.
In one embodiment of the invention the process includes the step of washing the catalyst-rich material in the filter with a solvent to recover residual desired hydrogenation product.
The pressure filter may be fitted with a removable filter bag and in this case the water wet catalyst is preferably removed from the bag and the bag is reusable. Alternatively the bag containing the catalyst is removed and sent for catalyst recovery.